Lift pump units

ABSTRACT

TORQUE LOAD FLUCTUATIONS ON THE PRIME MOVER OF OIL WELL PUMPS AND THE LIKE HAVING A ROTARY CRANK FOR DRIVING A WALKING BEAM ARE MINIMIZED THROUGH COUPLING OF THE PITMANS TO THE WALKING BEAM ALONG A MOVABLE LINE OF CONTACT BETWEEN ABUTTING BEARING SURFACES THAT ARE AFFIXED TO THE PITMANS AND THE BEAM RESPECTIVELY, AND THAT ARE HELD IN NONSLIDING ROLLING ENGAGEMENT WITH EACH OTHER, SO THAT THE LEVER ARM DISTANCE BETWEEN THE LINE OF CONTACT AND THE PIVOT AXIS OF THE WALKING BEAM VARIES AS THE ANGLE BETWEEN THE PITMANS AND THE BEAM CHANGES WITH ROTATION OF THE CRANK TO PROVIDE A GREATER MECHANICAL ADVANTAGE DURING THE POWER STROKE OF THE PUMP AND A LESSER MECHANICAL ADVANTAGE DURING ITS RETURN STROKE.

Nov. 23, 1971 Filed Aug. 28, 1969 w. s. MILLER 3,621,113

LIFT PUMP UNITS 5 Sheets-Sheet 1 W? A? 2, L5 74 o v v i i I I /&

mill! Li 254 30 A6 "7 2Q 52 i: 0 6 INVENTOR WENDELL s. MILLER Mil Nov. 23, 1971 w. s. MILLER 3,621,723

LIFT PUMP UNITS Filed Aug. 28, 1969 3 Sheets-$heet 2 22- 572 -i (/FSTEOKQE DflWA/STEOZZ ATTO A/EY Nov. 23, 1971 w, s, MlLLER 3,521,728

LIFT run? UNITS Filed Aug. 28, 1969 3 Sheets-s s 52 52 I 4 I I I 1y VENTOR WE/VDELL 5. M// L,Q,

BY M l United States Patent 3,621,723 LIFT PUMP UNITS Wendell S. Miller, 1341 Coinstock Ave., Los Angeles, Calif. 90024 Filed Aug. 28, 1969, Ser. No. 853,771 Int. Cl. F161! 21/32 US. CI. 74-41 8 Claims ABSTRACT OF THE DISCLOSURE Torque load fluctuations on the prime mover of oil well pumps and the like having a rotary crank for driving a walking beam are minimized through coupling of the pitmans to the walking beam along a movable line of contact between abutting bearing surfaces that are aflixed to the pitmans and the beam respectively, and that are held in nonsliding rolling engagement with each other, so that the lever arm distance between the line of contact and the pivot axis of the walking beam varies as the angle between the pitmans and the beam Changes with rotation of the crank to provide a greater mechanical advantage during the power stroke of the pump and a lesser mechanical advantage during its return stroke.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to single action lift pumps of the type employed for oil wells and the like, and more particularly to an improvement which permits modification of conventional oil well pumps to minimize torque load variations on the prime mover and to reduce whip on the rod string.

(2) Background of the invention Most deep well pumping units in present use, particularly for oil wells, employ a walking beam pivoted for rocking motion on a supporting Samson post. One end of the beam contains a horsehead attachment coupled to the rod string for alternately lifting and lowering a plunger located deep within the well. A rotary crank driven by a prime mover is coupled to the walking beam by pitmans to provide up and down docking motion. A counterbalance system, which is commonly a weight carried by the crank mechanism or an appropriate spring action pneumatic piston attached to the walking beam, is used to balance loads on the pump apparatus between the power and return strokes of the pump.

However, the prime mover of such conventional pumping units is still subject to undesirable torque load fluctuation since the torque due to the counterbalance has a regular sinusoidal variation, whereas the torque due to the well load during the lifting stroke differs substantially from that encountered during the return stroke. In such conventional units, the net torque on the prime mover goes to Zero at least twice during each complete cycle of the crank because as the well load torque reverses direction so does the counterbalance torque. Such torque fluctuations place considerable strain upon the pump mechanism and prevent the prime mover from operating at maximum efiiciency. In addition, the rod string in the well and its connection to the horsehead are subjected to a considerable whip as downward movement is rapidly reversed at the bottom of each cycle. This whip action subjects the rod string to considerable dynamic strain that can often result in structural fatigue and failure.

Past efforts to alleviate these shortcomings of such conventional pumping units resulted in the design of wholly new pumping units of the type described and illustrated in US. Pat. No. 3,029,650 issued Apr. 17, 1962, to

3,621,723 Patented Nov. 23, 1971 Joseph P. Byrd. These pumps have the crank offset between the supporting pivot on the Samson post and the horsehead end of the beam to provide a Whitworth type linkage that lengthens the duration of the lifting stroke while shortening the return stroke, and also causes the beam to reverse more slowly at the bottom of its return stroke then at the top of the lifting stroke to reduce the whip action. By proper placement of the crank relative to the point of connection of the pitmans to the beam, and selection of an appropriate crank to pitman ratio, the phase and amplitude relationships between the well load and counterbalance torques can be adjusted to minimize net torque fluctuations throughout the pump cycle. However, a system of this type, because of the offset placement of the crank, generates unusually heavy loads on the crank and pitman linkages, which for this reason must be specially constructed to withstand these forces. Also, existing conventional pump units generally cannot be adapted to this system so that an entirely new unit must be constructed and installed at each well site.

SUMMARY OF THE INVENTION In a pump in accordance with this invention, a movable coupling between connecting rod or pitmans and the walking beam varies the effective length of the lever arm relatively to the beam pivot axis. The movable coupling consists a first bearing surface aflixed to extend along the walking beam with a second bearing surface affixed to the connecting rod or pitmans. The two bearing surfaces are maintained in constant nonsliding rolling engagement to provide a movable line of contact between them, with at least one of the surfaces being curved to roll along the other so that the line of contact is shifted along the beam as the angle between the connecting rod and beam changes ,as the crank mechanism coupled to the other end of the connecting rod or pitmans rotates. The length of the lever arm between the line of contact and the beam pivot axis varies so that it is significantly longer during the power stroke of the pump than during the return stroke for each pivotal position of the beam. This prolongs the duration of the lifting stroke when the load is greater relative to the return stroke. With proper phasing of the counterbalance, a relatively even distribution of torque load on the prime mover can be achieved throughout the pump cycle. In addition, the reversal of beam direction at the completion of the return stroke may be made to occur at a relatively slower rate to reduce Whip on the rod string.

The advantages of the invention may be obtained by simple modification of existing conventional oil well pump units to provide the desired bearing surfaces necessary for the movable coupling between the walking beam and the pitmans. Proper selection of the shape and placement of the bearing surfaces relative to one another and to the beam pivot axis permits control of the pump stroke to achieve various desired modes of operation in minimizinz net torque variations on the prime mover and reducing whip on the rod string.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view illustrating a preferred form of a mechanical oil well pump in accordance with the invention, which has a balanced walking beam driven by a counterweighted rotary crank mechanism;

FIG. 2 is a diagrammatic representation of the operation of the pump unit of FIG. 1 showing successive operation relationships of the walking beam, crank and pitmans relative to the beam pivot axis and the crankshaft axis during a complete pump cycle;

FIG. 3 is a graphical representation illustrating th variation in the angle of the walking beam relative to the angular position 0 of the rotating crankshaft;

FIG. 4 is a graphical representation of the fundamental torque relationships existing during a complete pump cycle of a unit in accordance with this invention;

FIG. 5 is an enlarged side elevational view with outer portions broken away to show the interior operative elements of one form of a movable coupling between the pitmans and the walking beam, such as may be employed in the pump unit of FIG. 1;

FIG. 5a is a full sectional view of the movable coupling of FIG. 5 taken along the line 5a5a with selected portions broken away;

FIG. 6 is an enlarged side elevational view with outer portions broken away to show the interior operative elements of another form of movable coupling that may be employed for pump units in accordance with the invention;

FIG. 6a is a full sectional view taken along the lines 6a-6a of FIG. 6 with selected portions broken away;

FIG. 7 is an enlarged side elevational view of yet another form of movable coupling with the outer portions broken away;

FIG. 7a is a partial sectional view taken along the line 7a-7a of FIG. 7; and

FIG. 8 illustrates another form of pumping unit in accordance with the invention, which employes a front driven, unbalanced walking beam with a compensating pneumatic piston.

DETAILED DESCRIPTION Referring now to FIG. 1, which illustrates a preferred form of the invention as it is applicable to the widely used conventional oil well pumping units of the backdriven crank balanced walking beam type, an elongated walking beam 10 with a horsehead attachment 12 at its free end is journalled in a saddle bearing assembly 14 for rocking motion about a pivot axis on the upper end of Samson post support. Strut members 16 forming the Samson post have their upper ends joined at the pivot axis with the lower ends attached to a base structure 18. A prime mover 20, usually a gasoline engine, is attached on a motor mount 22 that is adjustably afi'ixed to the base r 18. Prime mover drives power pulley 24 that is coupled by a drive belt 26 to a larger diameter pulley 28 on a gear reducer 30 mounted on the base support 18 for driving a rotary crank mechanism on a crankshaft 32. A crank 34 mounted for rotation with the crankshaft 32 carries a counterbalance weight 36 at its outer end, and connecting rod or pitmans 38 has its lower end rotatably journalled in lower pitman bearings 40 at an intermediate point on the crank 34. The upper end of the pitmans 38 is coupled as hereinafter described to the power driven end of the walking beam 10 to effect the desired reciprocating beam movement. A flexible wire cable 42 has its upper end attached to the top of the horsehead 12 at the free end of the beam 10 to extend over its curved face, and its lower end engages a fitting 44 at the upper end of a polished rod 45 attached to the rod string that extends deep into the well casing for connection to the pump plunger or piston that lifts the oil or other liquid.

The aforementioned conventional elements of the well pump unit are not illustrated or described herein in detail since the details of their construction and operation are sufficiently well known to be unnecessary to a complete understanding of the invention. In fact, most of these pump elements, with the possible exception of the connecting rod or pitmans 38, may be those existing in prior conventional pump units of this type that are already installed and operating and are to be modified as hereinafter explained to provide an improved pump unit operating in accordance with the invention.

As distinguished from conventional oil Well pump units, in which the upper end of the pitmans is rotatably journalled at a fixed point on the walking beam, the improved pump action of this invention is achieved by use of a relatively simple movable coupling arrangement 46 between the upper end of the pitmans 38 and the driven end of the walking beam 10. As will be more fully apparent hereinafter in describing certain preferred forms, this movable coupling arrangement 46 can be implemented with any of a variety of coupling relationships. Basically, the movable coupling 46 consists of one structure 48- that defines a first bearing surface afiixed to the walking beam 10 with another structure 50 that defines a second bearing surface abutting the first carried on the upper end of the pitmans 38. At least one of the bearing surfaces is curved to provide rolling motion with respect to the other surface and to define a line of contact between the abutting bearing surfaces. The surfaces are maintained in nonsliding rolling engagement with one another so that the line of contact is shifted to vary the effective mechanical advantage.

In the FIG. 1 device the first bearing surface extends along the walking beam 10, and the structure 50 is carried in a fixed position on the upper end of pitman 38 so as to affect a change in the length of the lever arm provided by the position of beam 10 to the left of the pivot axis 15 as shown. More specifically, the beam bearing structure 48 provides a flat bearing surface with a straight gear rack 52 to engage a mating curved gear arrangement provided with a curved bearing surface on the pitman bearing structure 50. The load is borne along a line of contact between the opposing smooth bearing surfaces provided by the bearing structures 48 and 50 which are held against sliding movement by the engagement of the opposing gear racks adjacent these surfaces, as shown in the arrangements illustrated in FIGS. 5 and 6, or by some other means as illustrated in FIG. 7 which hereinafter are described in more detail.

Referring now to FIG. 2, a circle 54 represents the path described by the center axis of the lower pitman bearing 40 as it rotates clockwise about the axis of the crankshafts 32 at constant speed. The positions 0 through 7 represent successive loci of the lower pitman bearing axis during a full rotational cycle with the position at any point along the path being designated by the angular position of the cnank axis relative to the 0 locus point, which corresponds to the crank position with the driven end of the crank at its maximum upward position upon completion of the pump-down stroke. The corresponding successive positions of the line of contact between the bearing surfaces on the beam 10 at the upper end of the pitmans 38 are similarly designated by the successive positions 0 through 7 on the pump upstroke and downstroke curves 56 and 58, respectively, in the upper portion of this figure. The angular position of the walking beam 10 at each position along these curves during its rocking motion about the beam pivot axis 14 relative to the horizontal axis 60 is designated by the angle which is positive or negative depending on whether the driven end is above or below the horizontal. Lines 62 representing the pitmans connection between upper and lower pitmans bearings at each operating position 0 through 7'. Of course, in this embodiment, the driven end of the walking beam 10 moves downward along the curved path 56 during the pump upstroke resulting in the upward movement of the other end, whereas the driven end is moving upward along the path 58 during the pump downstroke.

As will be noted from the diagrams of FIGS. 2 and 3, the plain numbers positions 0, 1, 2, etc., through 7 represent successive crank loci at approximately equal 45 arcs around the crank circle 54, whereas the numbers having the prime designations 0, 4', 5, 6' and 7' represent selected crank positions approximately midway or 22 /2 between the plain number positions. During the pump upstroke the opposite free end of the beam is moved downward so that the other end lifts the fluid from the well, and the movable line of contact the bearing surfaces between the upper end of the pitmans 38 and the beam 10 traverses the downward curved path 56 from position 0 through position 5. Thus, the downstroke of this end requires more than a half of the crank rotaion cycle. During the return or downstroke of the pump, the line of contact moves upward by along the curved path 58 from position 5 back to position in less than half of a full crank rotation cycle. With the crank rotating at a constant rate to have a constant angular velocity, the work or lifting stroke, during which the pump load includes the weight of the fluid being lifted from the well, requires a significantly longer period for completion than the return or downstroke.

In achieving this result, it is noted that the movable contact line is closest to the beam pivot axis 14 to provide the shortest lever arm at position 5, and is farthest away to provide the longest lever arm at approximately position 1. At position 5, the angle of the pitman 38, as represented by the appropriate connecting line 62, with the walking beam 10 is greatest. As the crank 34 continues to rotate through positions 6 and 6', the beamto-pitmans angle slowly decreases as the free end of the beam tilts upward while the angle of the pitmans connecting line relative to the horizontal remains substantially constant. The line of contact moves slowly outward on the beam 10 as the curved bearing surface attached to the upper end of the pitmans 38 is rolled along the flat bearing surface on the beam member 48 outwardly along the beam 10. After position 6, the rate of decrease of the beam-to-pitmans angle accelerates until reaching position 0 since the lower end of the pitmans is being moved both upwards and laterally to the right so that the beamto-pitmans angle changes more rapidly.

During the initial portion of the downstroke from positions 0 to 0', the lateral movement of the crank 34 to the right is relatively large compared to its vertical movement. This further decreases the beam-to-pitman angle to effect a further lengthening of the available lever arm, and between positions 0', and 1 this angle only slightly decreases greater downward movement of the crank 34 and the beam 10. From position 1 to position 2 the crank movement is mostly downward so that the pitmans-to-beam angle remains substantially constant. However, past position 2 the crank moves downward and towards the left, and with the downward movement of the beam 10, the pitmans-tobeam angle rapidly increases causing movement of the line of contact inward along the beam to quickly decrease the available lever arm length from its maximum to its minimum at position 5. Note that during the pump work or upstroke the angle between the beam and pitmans is smaller for each position of the beam 10 than during the return or downstroke so that the line of contact is rolled further out on the beam to provide a longer lever arm for handling the heavier pump load on the upstroke when the fluid is being lifted.

The reversal of the pump direction at the end of the downstroke is accomplished relatively slowly taking place over an approximately 45 arc of crank movement from positions 7' to 0 and so as to reduce whip on the rod string. During this reversal the walking beam traverses a relatively small angle compared with the angle traversed at the end of the upstroke during movement of the crankshaft through-a corresponding angular extent from positions 4' to 5'. Accordingly, the severe whip on the rod string at the end of the downstroke usually associated with conventional balanced beam pump units is significantly reduced.

The advantageous results achieved are best seen by reference to FIG. 3 in which the variation of the angle 5 of the walking beam 10 relative to the horizontal reference line 60 is plotted with respect to the angle 0 of crank rotation from the initial 0 position. During the pump working or upstroke from position 0 through approximately 225 of crank rotation to position 5, it is noted that the variation in the beam angle as has a relatively gradual average slope downwards to the position point 5 as compared with the sharp upward slope in the initial portion of the return or downstroke from positions 5 to point 0. a a a Referring now to FIG. 4, the effect of pump action achieved by this arrangement is to reduce load variations on the prime mover 20 and the reduction gear train 30 throughout the pump cycle. The torque produced by the counterbalance weight 36 has a pure sinusoidal variation as represented by the curve 70, which for the purposes of this illustration is shown inverted to more clearly show the net torque relationship. The counterbalance torque curve crosses the zero torque axis twice each cycle of crank rotation at 191% and at 11%, where the center of gravity of the crank weights is vertically upward or vertically downward and thus produce no torque. Maximum counterbalance torques are produced when the counterbalance weight is horizontal on either side of the crankshaft axis 32, and these maximum counterbalance torques occur at approximately 101%" and 281% in a cycle of crank rotation. The addition or subtraction of weights from the counterbalance: on the crank merely varies the amplitude and perhaps the phase of this curve, but is remains a pure sinusoidal shape.

The well load torque is represented by a curve 72 that is nearly sinusoidal but is displaced upward from the curve 70. The prolongation of the pump upstroke not only reduces the peak torque required since it is spread out over a longer period of time, but also places the zero torque axis crossings of the pump load curve 72 on opposite sides of the zero axis crossings for the counterbalance torque curve 70, and the peak pump load torque in both positive and negative directions is phased to correspond approximately with the phasing of the peak counterbalance torques at l0l A and 281%".

By subtracting the instantaneous values of counterbalance torque 70 from the corresponding values of the pump load torque 72 throughout the pump cycle, a curve representing the net torque on the gear reducer and prime mover may be plotted. In an ideal situation, this net torque is represented by the straight horizontal dashed line 74, while actual torque variation in a typical unit of this type is more accurately represented by the curved line 76. Although variations in the actual net torque as shown by the curve 76 still occur, the amplitude of these variations is significantly reduced relative to the conventional balance beam units, and in addition the peak net torque loads are significantly smaller and the net torque maintains a positive value throughout each crank cycle.

Referring now to FIGS. 5, 6 and 7, the movable coupling arrangement between the upper end of the pitmans 38 and the walking beam 10 may be implemented in various forms to provide the desired nonsiliding rolling engagement between bearing surfaces on the pitmans 38 and the walking beam 10. In the arrangement of FIGS. 5 and 5a a pair of channels 74 are clamped by the bolt 76 on opposite sides of a central block member 78 having a gear rack formed along its upper surface. The channels 74 may form part of the walking beam 10, or be attached as extensions to an existing walking beam structure. An axle member '80 is bolted on either end to extend between the upper ends of the pitmans 38 on either side of the channels 74 and the central block member 78, and is held against rotation relative to the pitmans 38 by keys 82 inserted to engage opposing slots. A pair of circular rollers 84 are rotatably mounted on either side of a central pinion 86 that is held against rotation by the key 87 inserted in opposing slots on the axle and pinion 86. Gear teeth are provided around at least the lower portion of the pinion 86 to engage the gear teeth on the upper surface of the rack member 78. The bearing load is supported along the line of contact between the abutting surfaces of the circular rollers 84 and the upper surfaces of the channels 74, whereas the mating gear teeth of the pinion 76 and the rack member 78 are maintained in engagement only to the extent necessary to force rolling motion of the roller bearings 84 along the channels 74 as the pitmans-to-beam angle changes.

In another form shown in FIGS. 6 and 6a, an axle 88 mounted between the upper ends of-the pitmans 38 is keyed against rotation and has formed thereon a central roller bearing surface between surrounding geared pinion sections 90 formed on either side. The geared pinion sections 90 engage a gear rack mounted on the upper surfaces of the channels 74 that are attached on either side of a box beam 92. The upper surface of the box beam 92 provides a hat roller surface for supporting the abutting roller surface of the axle 88. As before, the pinion gear teeth on the outer sections 90 engage the gear teeth on the rack 94 only to the extent necessary to constrain rolling action along the upper surface of the box beam 92. In this case, the diameter of the roller section of the axle 88 should be equal to the pitch diameter of the geared pinion sections 90.

As shown in FIGS. 7 and 7a, the type of rolling action desired may be achieved by means other than the geared rack and pinion arrangements. In this case, a roller 96 is mounted on an axle between the upper ends of the pitmans 38 to contact the upper surface of the walking beam 10, which in this case consists of the box beam 97. A curved rocker member 98 is mounted on the axle on either side of the roller 96 with a key inserted to prevent rotation relative to the pitmans 38. The curved rocker member 98 in this case has a semicircular face with grooves formed therein for receiving restraining cables 100 with one end attached to the beam 97 and the other end to the top of the rocker member 98. The cables are tensioned along the beam 97 from opposite sides to curve upward along the respective slots over the curved face of the rocker 98. In this way, the cable restrained rocker arrangement maintains the curved lower surface of the roller 96 in constant nonsliding rolling engagement with the fiat surface of the beam 97.

Of course, the variation and the lenth of the lever arm along the walking beam 10, or any given variation in the pitman-to-beam angle for each of the above described movable coupling arrangements is directly proportional to the radius of curvature of the curved bearing surface on the pitmans. More generally, the movement of the point of contact between the bearing surfaces to change the length of the lever arm may be varied by changing the shape and size of the adjacent surfaces. Either of the bearing surfaces may be made straight or curved, or both may be curved, depending upon the particular result desired. However, the particular arrangement shown in which the pitmans bearing surfaces are curved to roll along a straight beam bearing surface is preferable from the standpoint of simplicity, and the length of the beam lever arm may be made to change more quickly or more slowly during certain portions of the crank cycle merely by varying the curvature of the pitmans bearing surface.

Referring now to FIG. 8, the principles of this invention may be adapted to improve the operation of conventional air balanced pump units that use an unbalanced walking beam 110 pivotally mounted at one end for rocking motion in a saddle bearing 116 at the top of a Samson post 114. In these units, the reducer 30 is mounted forward of the Samson post and drives the crank arm 34 that does not carry a counterbalance weight. Instead, the counterbalance is provided by a compressed air unit 116 within which a piston moves in a cylinder on the downstroke to compress the air within the unit to provide an upward force that counterbalances the well load during the upstroke. Although conventional air balanced pumping units of. this type reduce net torque loads on gears and prime movers, the operation is further improved by use of a movable coupling arrangement in accordance with the invention. The operation of such a unit need not be described in detail since it should be obvious the principles of the invention permit the reduction of net torque variations by lengthening the period of the work stroke or upstroke relative to the return or downstroke, and also provide some improvement in slowing the reversal of pump direction at the end of the downstroke.

However, with the air balanced pumping units the upwards counterbalance force remains substantially constant so that there is not the sinusoidal counterbalance torque provided by a counterbalance weight. As a result, the pump and counterbalance torque curves cannot be phased exactly to prevent the net torque resultant from reaching zero or going negative. For this reason, the curved bearing at the upper end of the pitmans 38 should be provided with an upper roller bearing surface to maintain constant contact between the bearing surfaces of. the pitmans 38 and the walking beam 110. However, only a single gear rack 122 is necessary for maintaining the nonsliding rolling engagement between the bearing surfaces.

What is claimed is:

1. In an apparatus of the reciprocating type having a work stroke and a return stroke, the improvement comprising:

a lever beam mounted for reciprocating rocking motion about a pivot axis to produce said work and return strokes during movements in opposite directions and having a first bearing surface distal said pivot axis;

a rotary crank mechanism; and

a connecting rod coupling said rotary crank mechanism to said lever beam, said connecting rod including a second bearing surface maintained in continuous nonsliding rolling engagement with said first bearing surface along a line of contact parallel to said pivot axis, at least one of said bearing surfaces having a curvature to provide nonsliding rolling motion along the other bearing surface to move the line of contact along said beam relative to said pivot axis as the angle between said connecting rod and said lever beam varies whereby the distance between said line of contact and said pivot axis is greater during the work stroke than during the return stroke for each corresponding position of said lever beam.

2. The improvement of claim 1 wherein: said first bearing surface has a substantially planar configuration extending along the length of said lever beam towards said pivot axis, and said second bearing surface has a substantially circular convex curvature. I 3. The improvement of claim 2 wherein: said first and second bearing surfaces contain interlocking gear teeth disposed thereon to provide nonsliding engagement therebetween. 4. The improvement of claim 1 wherein: crank mechanism rotates about an axis located along a line substantially normal to said lever beam at a point along said first bearing surface when the lever beam is at the midpoint of each. stroke. 5. A device for producting reciprocating lifting and return movement of a plunger comprising:

post support means; an elongated beam pivotally mounted on the post support means for rocking motion in a substantially vertical plane about a pivot axis; means depending from a movable end of the beam adapted to be connected to the plunger; a prime mover; a crankshaft operatively connected to be rotated at a substantially constant speed by the prime mover; an elongated crank affixed to said crankshaft and extending axially outward for rotation about the crankshaft axis; counterbalance means carried by said crankshaft for rotational movement around the crankshaft axis opposite said crank; pitmans having one end rotatably journalled for movement by said crank about said crankshaft; variable coupling means for operatively connecting the other end of said pitmans opposite said crank to said elongated beam along a line of contact parallel to said pivot axis for imparting cyclical rocking motion to said beam, said means comprising nonslidably engaged abutting first and second contact surfaces, the first surface fixedly positioned at the end of said pitmans opposite said crank and the second surface being fixedly positioned on said beam to extend along its axis of elongation, one of said surfaces having a degree of curvature greater than the other surface to provide rolling nonslidable movement of said one surface along said other surface to vary the position of said line of contact along said beam so that the distance between said line of contact and said pivot axis during lifting of said plunger is substantially greater than during return of said plunger for each angular position of said beam.

6. In an apparatus of the reciprocating pump type having a work stroke and a return stroke, the improvement comprising:

a lever beam mounted for reciprocating rocking motion about a pivot axis to produce said work and return strokes during movements in opposite directions and having a first contact means fixedly mounted distal said pivot axis to provide a first contact surface extending along said lever beam normal to said pivot axis;

a rotary crank mechanism; and,

a connecting rod coupling said rotary crank mechanism to said lever beam, said connecting rod fixedly mounting second contact means having a second contact surface maintained in continuous engagement with said first contact surface to establish a point of contact movable along first contact surface relative to said pivot axis, at least one of said contact surfaces being curved and maintained in nonsliding rolling engagement with the other contact 35 surface to move the point of contact longitudinally lll along said beam relative to said pivot axis as the angle between said connecting rod and said lever beam varies, whereby the distance between said point of contact and said pivot axis is greater during the Work strokes than during the return strokes for each corresponding position of said lever beam.

7. The improvement of claim 6 further comprising:

a first bearing member having a bearing surface carried by said lever beam to extend normal to said pivot axis; and,

second bearing means carried by said connecting rod and movable with said point of contact along said first bearing surface for transmitting forces applied to said connecting rod to said lever beam.

8. The improvement of claim 6 wherein:

said first contact means constitutes a first bearing surface extending along said lever beam normal to said pivot axis; and,

said second contact means constitutes a second bearing surface maintained in continuous nonsliding rolling engagement with said first bearing surface, the force applied to said connecting rod being transmitted to said lever beam adjacent said movable point of contact.

References Cited UNITED STATES PATENTS 118,572 8/1871 Young 7442 836,601 11/1906 Nelson 74--42 2,272,579 2/1942 Perry 74--41 WILLIAM F. ODEA, Primary Examiner W. S. RATLIFF, JR., Assistant Examiner US. Cl. XR. 

